Journal Articles (before-1995)

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    Magnetic Studies of Zeolites: Part 2.—Magnetic Properties of NiA, NiX and NiY
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (1), 1973) Egerton, T. A.; Vickerman, J. C.
    The bulk susceptibilities of nickel-cxchanged forms of zeolites A, X and Y measured over a wide range of temperature show that in the fully hydrated zeolites the nickel ions arc octahedrally coordinated. On dehydration, the octahedral coordination is retained by the nickel ions of NiA and NiCaX. However, highly dehydrated NiA was found to be unstable. For NiX and NiY, the reciprocal susceptibility passed through a maximum when the number of residual water molecules were 4 to 6 per Ni2+ ion. This is believed to arise from a distorted octahedral or pentahedral coordination around the Ni2+ ions, where some of the ligands are residual water molecules and the other ligands are lattice oxygen ions. Further dehydration causes a decrease in the reciprocal susceptibility, this being attributed to many of the Ni2+ ions being in tetrahedral coordination, where three of the ligands arc lattice oxygen and the fourth is derived from residual water. A tendency for Ni2+ to occupy the hexagonal prisms in preference to sites I' and IF is evident in dehydrated CaNiX but not in NiX or NiY. The Ni2+ ions may move out of the hexagonal sites of dehydrated NiX, NiY and CaNiX at T>400 K ; this behaviour is reversible. We suggest that where most of the Ni2+ ions in a dehydrated zeolite arc tetrahedrally coordinated, the nickel ions arc less susceptible to reduction.
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    Magnetic Studies of Zeolites: Part: 1.—The Magnetic Properties of CoY and CoA
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (4), 1972) Egerton, T A; Hagan, A; Stone, F S; Vickerman, J C
    The bulk susceptibilities of cobalt-exchanged zeolites Y and A have been measured over a wide range of temperature using an enclosed Gouy balance. The magnetic properties indicate that the cobalt ions arc octahedrally coordinated in fully hydrated CoY. On dehydration, the reciprocal susceptibility rises and reaches a maximum when the number of residual water molecules approximately equals the number of cobalt ions. Further dehydration causes the reciprocal susceptibility to fall. It is believed that the maximum in the reciprocal susceptibility corresponds to most cobalt ions being in a tetrahedral or near tetrahedral environment. This coordination is provided by three oxygens from the zeolite framework together with one oxygen from a residual water molecule. Further dehydration removes the remaining water molecules and the final fall in reciprocal susceptibility indicates a migration of the cobalt ions from the tetrahedral coordination to the octahedral coordination associated with the hexagonal prisms of the framework. The behaviour of CoA is broadly similar to CoY in the initial stages of dehydration. However, there is no fall in the reciprocal susceptibility during the final stages of dehydration. Since there are no hexagonal prisms in the zeolite A structure, the absence of a final decrease of reciprocal susceptibility supports the interpretation of the CoY results.